Some diseases and disorders are always in focus because people die rapidly form them. Then there are slow and hidden killers that cost many life-years but only rarely get attention. Now a group of researchers has analysed the mortality rates for 39 categories of health conditions. However, the purpose is not to attract headlines, because pinpointing the most fatal diseases is not that easy. The goal is to provide other researchers with a tool to gain insight into these diseases and disorders and to serve as a benchmark for evaluating future initiatives for treatment and prevention.
The mortality rate is the number of deaths per 1000 population from specific diseases and disorders and arguably the most definitive measure of health. How many people die from or with which diseases is very important as a basis for setting priorities for allocating healthcare resources. However, determining the relative risk associated with mortality may be even more important. How much earlier do people with certain diseases die – that is, how many total years of life lost are associated with various diseases? A group of researchers has now examined this using 39 health condition categories based on the World Health Organization’s International Classification of Diseases (ICD-10).
“We used Denmark’s health registries to identify all the people who have had 39 diseases and disorders of a total of 1803. This provides a new overview of which ones people die from and with but also which are associated with the most years of life lost. This may help other researchers in finding important areas to examine more closer and health authorities to set priorities for their efforts and to measure the effects,” explains a lead author, Oleguer Plana-Ripoll, Associate Professor, Department of Clinical Medicine, Aarhus University.
Death rarely has one cause
Many studies have focused on mortality, but none has covered all known diseases and disorders at once. Nor have the studies examined variation in age of onset. The researchers are trying to rectify this with the new Danish Atlas of Disease Mortality, which is based on anonymised data from Denmark’s nationwide health registries.
“Previous studies focused on either relative measures of mortality or approximate estimates of life expectancy. Using a new method, we measured mortality more accurately than before for the more than 1800 diseases and disorders by using data from 7.4 million people in Denmark from 2000 to 2018. Including the age of onset of various diseases enables us to connect different types of mortality estimates and thus provide a richer and more nuanced understanding of the relationship between diseases and disorders and mortality,” says Oleguer Plana-Ripoll.
Oleguer Plana-Ripoll says that determining which diseases and disorders are the most fatal is not that straightforward, because death rarely has a single primary cause. Some diseases and disorders often lead to others, such as diabetes or mental disorders. In addition, this determination depends on whether it is based on the risk of dying or the total years of life lost.
“Some diseases that arise late in life, such as cancer, have a relatively high mortality risk but are not as significant overall based on the years of life lost. Conversely, many diseases with onset among younger people are associated with more years lost, even though they may have a relatively lower risk of mortality,” explains Oleguer Plana-Ripoll.
For example, circulatory diseases such as atherosclerosis and heart attacks have a very high mortality rate, but since they typically affect very old people, few years of life are lost.
“So even if the headlines would be more appealing, making a list of the most deadly diseases is misleading because it is open to interpretation. The purpose of our research is not to provide simple answers but to provide the best possible starting-point for in-depth study by others,” says Oleguer Plana-Ripoll.
How can we maximise life-years?
The method behind the study stems from the researchers’ previous studies of mental disorders, which typically cost many years of life lost. The lesson, however, was that the age at which a mental disorder begins strongly influences the years of life lost among those who develop the disorder.
“Previous studies estimating life expectancy assumed a fixed baseline age of 15 years for those with a mental disorder and 55 years for people with colon cancer, but these simplified assumptions deviate significantly from the actual life expectancy we can determine. We hope that our new atlas can give other researchers a more fine-grained analysis of the association between a comprehensive set of diseases and disorders and mortality-related estimates and thus a better starting point for determining which associations are worth investigating,” explains Oleguer Plana-Ripoll.
Oleguer Plana-Ripoll emphasises that the data are only a starting point. For example, the data show lower mortality than normal for women who have developed diseases during pregnancy. At first glance, this seems illogical, but according to Oleguer Plana-Ripoll, this emphasises the importance of not drawing unnecessary conclusions from the numbers. Nevertheless, he hopes that doctors, health authorities and politicians can benefit greatly from the accompanying interactive data visualisation website that is open to everyone.
“Measures for the mortality from disease can be used in making decisions and setting priorities for allocating healthcare resources. How can we minimise the years of life lost by using the fewest resources overall? Used properly, the Atlas could become a very effective tool in health research and serve as a basis for comparison for future health initiatives by examining whether various interventions are associated with reduced or increased mortality,” concludes Oleguer Plana-Ripoll.